Present-day Internet communications represent the synthesis of technical developments begun in the 1960s. During that time period, the Defense Department developed a communication system to support communications between different United States military computer networks, and later a similar system was used to support communications between research computer networks at United States universities.
The Internet
The Internet, like so many other high tech developments, grew from research originally performed by the United States Department of Defense. In the 1960s, Defense Department officials wanted to connect different types of military computer networks. These different computer networks could not communicate with each other because they used different types of operating systems or networking protocols.
While the Defense Department officials wanted a system that would permit communication between these different computer networks, they realized that a centralized interface system would be vulnerable to missile attack and sabotage. To avoid this vulnerability, the Defense Department required that the interface system be decentralized with no vulnerable failure points.
The Defense Department developed an interface protocol for communication between these different network computers. A few years later, the National Science Foundation (NSF) wanted to connect different types of computer networks located at research institutions across the country. The NSF adopted the Defense Department's interface protocol for communication between the research computer networks. Ultimately, this combination of research computer networks would form the foundation of today's Internet.
Internet Protocols
The Defense Department's interface protocol was called the Internet Protocol (IP) standard. The IP standard now supports communication between computers and networks on the Internet. The IP standard identifies the types of services to be provided to users and specifies the mechanisms needed to support these services. The IP standard also describes the upper and lower system interfaces, defines the services to be provided on these interfaces, and outlines the execution environment for services needed in this system.
A transmission protocol, called the Transmission Control Protocol (TCP), was developed to provide connection-oriented, end-to-end data transmission between packet-switched computer networks. The combination of TCP with IP (TCP/IP) forms a system or suite of protocols for data transfer and communication between computers on the Internet. The TCP/IP standard has become mandatory for use in most packet switching networks that connect or have the potential for utilizing connectivity across networks or sub-network boundaries.
A computer operating on a network is assigned a unique physical address under the TCP/IP protocols. This is called an IP address. The IP address can include: (1) a network ID and number identifying a network, (2) a sub-network IP number identifying a substructure on the network, and (3) a host IP number identifying a particular computer on the sub-network. A header data field in the information packet will include source and destination addresses. The IP addressing scheme imposes a sensible addressing scheme that reflects the internal organization of the network or sub-network.
A router is located on a network and is used to regulate the transmission of information packets into and out of computer networks and sub-networks. A router interprets the logical address of an information packet and directs the information packet to its intended destination. Information packets addressed between computers on the sub-network do not pass through the router to the greater network, and as such, these sub-network information packets will not clutter the transmission lines of the greater network. If data is addressed to a computer outside the sub-network, the router forwards the data onto the greater network.
The TCP/IP network includes protocols that define how routers will determine the transmission path for packets through the network. Routing decisions are based upon information in the IP header and entries in a routing table maintained on the router. A routing table possesses information for a router to make a determination on whether to accept the communicated information packet on behalf of a destination computer or pass the information packet onto another router.
The routing table can be configured manually with routing table entries or with a dynamic routing protocol. In a dynamic routing protocol, routers update routing information with periodic information packet transmissions to other routers on the network. The dynamic routing protocol accommodates changing network topologies, network architecture, network structure, layout of routers, and interconnection between hosts and routers.
The IP-Based Mobility System
The Internet protocols were originally developed with an assumption that Internet users would be connected to a single, fixed network. With the advent of portable computers and cellular wireless communication systems, the movement of Internet users within a network and across network boundaries has become common. Because of this highly mobile Internet usage, the implicit design assumption of the Internet protocols has been violated.
In an IP-based mobile communication system, the mobile communication device (e.g. cellular phone, pager, computer, etc.) can be called a mobile node. Typically, a mobile node maintains connectivity to its home network through a foreign network. The mobile node will always be associated with its home networks for IP addressing purposes and will have information routed to it by routers located on the home and foreign networks. The routers can be referred to by a number of names including Home Agent, Home Mobility Manager, Home Location Register, Foreign Agent, Serving Mobility Manager, Visited Location Register, and Visiting Serving Entity.
Authenticate, Authorize, and Accounting
In an IP-based mobile system, the mobile node maintains its connectivity to the home system through a foreign network. While coupled to a foreign network, the mobile node will be assigned a temporary IP address, so information packets addressed to the mobile node can be routed to the temporary EP address for the mobile node on the foreign network.
When a mobile node is operating on a foreign network, specialized servers are used to authenticate, authorize, and collect accounting information for services rendered to the mobile node. This authentication, authorization, and accounting activity is called “AAA,” and AAA computer servers on the home and foreign network perform the AAA activities.
Authentication is the process of proving one's claimed identity, and security systems on a mobile IP network will often require authentication of the system user's identity before authorizing a requested activity. The AAA server authenticates the identity of an authorized user and authorizes the mobile node's requested activity. Additionally, the AAA server performs the accounting functions by tracking usage on the network.
Functionally, a mobility manager will communicate with the AAA server in the current domain, allocating another router to route information packets destined for a mobile node while it is located away from its home sub-network. The mobility manager may have access to authentication and key generation AAA functions to authenticate and generate session keys. The mobility manager may also perform agent functions to forward packets to the mobile node until registration is completed.
IP Mobility Protocol
During the formative years since the Internet was first established, Internet Protocol version 4 (IPv4) was recognized and adopted as the standard Internet protocol. With the advent of mobile IP and proliferation of computers and computer systems linked to the Internet, various limitations in the IPv4 standard and associated procedures have developed and emerged. The most pressing limitation in IPv4 is the restriction on number of IP addresses. As shown in FIG. 1B, the address field size in an IPv4 packet is only 32 bits.
A number of benefits emerge from having a larger address field. First, there is little chance of exhausting the number of possible IP addresses. Second, a large address field allows aggregation of many network-prefix routers into a single network-prefix router. Finally, large addresses allow nodes to auto configure using simple mechanisms. More efficient system designs are thus possible with an expanded address space. Thus, there is a need for an IP standard with a larger IP address space.
In wireless IP networks and sub-networks (divisions of a network), mobile nodes can be physically located anywhere on the network or sub-network. Wireless IP networks handle the mobile nature of mobile nodes with power-up and hand-off procedures designed to inform the mobile node's home network and sub-network of the location of the mobile node for packet routing purposes. Because mobile nodes can move within sub-networks and between networks, hand-off procedures need to be implemented to insure that packets are continually routed to the mobile node as it moves from one network to another or from one sub-network to another.
Current protocols for obtaining a care-of address and procedures for power-up registration and hand-off procedures are insufficient to handle current packet-based communication demands. For example, the prior power-up and hand-off protocols utilize system architecture that was designed to operate within the constraints of IPv4's limited address space. These constraints are insufficient for supporting a standard that needs a larger address space and the associated network design architecture. Therefore, a need exists to establish a new user protocol for power-up and hand-off procedures for mobile IP networks using an expanded address space.
A new protocol for power-up and hand-off is also needed to satisfy the following criteria:
1) Data transfer to a given mobile node should not be hampered by the introduction of additional functional architecture,
2) The new protocol should require only minimal extensions and should exploit and track evolving routing and addressing capabilities,
3) The new protocol should be generic and independent of the type of wireless technology or access medium,
4) The protocol should fully support and be consistent with an AAA architecture,
5) The new protocol should optimize air interface usage for efficiency, reducing the number of required overhand messages, such as Binding Update and Binding Acknowledgement messages, and
6) The protocol should also offer protection against over-use or monopolization of resources by certain mobile nodes.